EFFECT OF HYPOPHYSECTOMY ON PROLIFERATIVE ACTIVITY OF NORMAL AND MALIGNANT TISSUE

After hypophysectomy the thymidine-H-3 labeling index in hormone-dependent organs (adrenals) and parenchymal organs (liver, kidney) is significantly lowered. Unlike the cells of hormone-dependent organs, the liver cells are capable of compensatory growth even after hypophysectomy, but the presynthetic G1 period of their cycle is prolonged. In diethylnitrosamine-induced hepatocellular carcinomas the thymidine-H-3 labeling index and the mitotic index are much higher than they are in normal liver. Both indices drop within 15 days after hypophysectomy. The generation-time and cycle-phases indicate a fast mode of proliferation for hepatocellular carcinomas. Hypophysectomy slows the whole cell cycle, the G1 period being most affected. After hypophysectomy, that phase is extended by a factor of 4,5. Apparently even hepatocellular carcinomas require a de novo synthesis of specific RNA and protein molecules in the G1 period prior to every S-phase. The synthesis is accelerated by somatotropic hormone. In the absence of the pituitary synthesis is slowed in tumor cells too. © 1969 Springer-Verlag.